1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same and, more particularly to a capacitor having a metal electrode and a method of fabricating the same.
2. Description of the Related Art
Semiconductor memory devices such as dynamic random access memory devices (DRAMs) store data in a capacitor of a unit cell. The unit cell of the DRAM includes one access transistor and one cell capacitor that are serially connected. However, as DRAM devices continue to become increasingly integrated, the circuit area that is to be occupied by the unit cell is remarkably reduced, so that the capacitance of the capacitor is likewise reduced. The capacitance of the capacitor represents data storage capacity. When the capacitance of the capacitor is small, reading errors may occur during a read operation of stored data. Therefore, a capacitor with relatively high capacitance is required to maintain high performance in the DRAM device.
Typically, in order to implement a capacitor with high capacitance, a material having a high dielectric constant such as Ta2O5 or BST ((Ba,Sr)TiO3) is used as a dielectric layer material. However, in the case where such materials are used as a dielectric layer, it is difficult for a polysilicon layer, which is a common electrode material, to be used as a capacitor electrode. This is because when the thickness of the dielectric layer is reduced, tunneling occurs in the device, in turn causing leakage current. For these reasons, when a high-k dielectric layer or a ferroelectric layer is used as a dielectric layer, noble metals with a low work function such as platinum Pt, ruthenium Ru, iridium Ir, rhodium Rh, or osmium Os are used as capacitor electrode materials. Of these, ruthenium Ru has an advantageous property in that it is easily etched by plasma containing oxygen, and thus is widely used as upper and lower electrodes of a metal-insulator-metal (MIM) type capacitor.
However, in the MIM type capacitor, when a noble metal such as ruthenium Ru is used as a lower electrode, the lower electrode is commonly formed by depositing the ruthenium using a chemical vapor deposition (CVD) technique or an atomic layer deposition (ALD) technique to improve step coverage. In the CVD or ALD technique, oxygen is added as a process gas to improve layer characteristics such as morphology. However, when the lower electrode layer contains oxygen, this oxidizes a surface of a contact plug at an interface with the contact plug. Thus, an oxidation reaction occurs at the interface, thereby increasing contact resistance.